1. Field of the Invention
This invention relates to an attachment lens which may be mounted on the image side of a photographic lens to enlarge the focal length thereof, or a so-called rear conversion lens.
2. Description of the Prior Art
An attachment lens of this type which has heretofore been commercially available provides a negative lens system having a strong power and therefore, the Petzval sum thereof becomes negative, as a result of which the astigmatic difference between the sagittal plane and the meridional plane is particularly great, and accordingly, the other aberrations are also great. It may thus be said that a lens system having a conversion lens of such type mounted thereto to increase the focal length of the lens system is considerably inferior in performance to a fixed lens having a focal length equivalent thereto.